HTTP status codes. Setting status of an HTTPServletResponse

Size: px

Start display at page:

Download "HTTP status codes. Setting status of an HTTPServletResponse"

Eleanore Owens
6 years ago
Views:

1 HTTP status codes Setting status of an HTTPServletResponse

2 What are HTTP status codes? The HTTP protocol standard includes three digit status codes to be included in the header of an HTTP response. There are five classes of response statuses, identified by the first digit of the status code (with examples below): 1xx Informational 101 Switching Protocols (server agrees to switch) 2xx Success 200 OK 3xx Redirection 301 Moved Permanently 4xx Client Error 404 Not Found 5xx Server Error 500 Internal Server Error (something bad happened)

3 Setting the status in a Servlet If your servlet succeeds in sending the response to the client, you can set the HTTP status code like this: response.setstatus(httpservletresponse.sc_ok); If your servlet runs into any trouble, you should let the client know, by sending an appropriate status code (which you should document), e.g.: HttpServletResponse.SC_NOT_FOUND What code to send depends on the type of problem of course.

4 If your servlet is an API for data If your servlet is an API for getting data as e.g. Json, you should document the behaviour on the API documentation page. You can use SC_NOT_FOUND if the data cannot be served because it doesn t exist. You can also send an error message encoded as Json: StringBuilder page = new StringBuilder(); response.setstatus(sc_not_found); // needs import static... page.append("{studentapierror:\"").append(nsse.getmessage()) // you can include exception messages if you want.append("\""); out.println(page); out.close();

5 Example - student data API error - not found $ lwp-request -m GET {studentapierror:"no such student with ID: 666" $ lwp-request -m HEAD Not Found Connection: Keep-Alive Date: Thu, 26 Jan :37:39 GMT Server: Winstone Servlet Engine v Content-Length: 49 Content-Type: application/json Client-Date: Thu, 26 Jan :37:39 GMT Client-Peer: :8080 Client-Response-Num: 1 X-Powered-By: Servlet/2.5 (Winstone/0.9.10)

6 Example - student data API error - parameters $ lwp-request -m HEAD Bad Request Connection: Keep-Alive Date: Thu, 26 Jan :39:12 GMT Server: Winstone Servlet Engine v Content-Length: 59 Content-Type: application/json Client-Date: Thu, 26 Jan :39:11 GMT Client-Peer: :8080 Client-Response-Num: 1 X-Powered-By: Servlet/2.5 (Winstone/0.9.10) $ lwp-request -m GET {name: "JSONRequestError",message: "missing id parameter"

7 Example - student data API error - parameters public void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException{ String id = request.getparameter("id"); if(id!=null){ response.setcontenttype("application/json"); PrintWriter out = response.getwriter(); try{ printresult(out,id); catch(nosuchstudentexception nsse){ StringBuilder page = new StringBuilder(); response.setstatus(sc_not_found); page.append("{studentapierror:\"").append(nsse.getmessage()).append("\""); out.println(page); out.close(); else{ printerror(response); // Missing required ID parameter

8 Example - student data API error - parameters // Handles the missing ID parameter response private void printerror(httpservletresponse response)throws IOException{ response.setcontenttype("application/json"); response.setstatus(sc_bad_request); PrintWriter out = response.getwriter(); out.print("{name: \"JSONRequestError\","); out.println("message: \"missing id parameter\""); out.close();

9 Normal response $ lwp-request -m GET #valid call with existing ID { "studentname":"edward Eriksson", "studentid":"5", "courses":[ { "coursecode":"tig058" ] $ lwp-request -m HEAD OK Connection: Keep-Alive Date: Thu, 26 Jan :46:41 GMT Server: Winstone Servlet Engine v Content-Length: 0 Content-Type: application/json Client-Date: Thu, 26 Jan :46:41 GMT Client-Peer: :8080 Client-Response-Num: 1 X-Powered-By: Servlet/2.5 (Winstone/0.9.10)

10 Links

Servlet for Json or CSV (or XML) A servlet serving either Json or CSV (or XML) based on GET parameter - This version uses org.json

Servlet for Json or CSV (or XML) A servlet serving either Json or CSV (or XML) based on GET parameter - This version uses org.json A Servlet used as an API for data Let s say we want to write a Servlet